Compost Application Affects Metal Uptake in Plants Grown in Urban Garden Soils and Potential Human Health Risk

Purpose This study explores the effect of varying organic matter content on the potential human health risk of consuming vegetables grown in urban garden soils. Materials and methods Metal accumulation among edible tissues of green bean (Phaseolus vulgaris L.), lettuce (Lactuca sativa L.) and carrot (Daucus carota L.) was determined for plants grown in five urban garden soils amended with 0, 9, or 25% (v/v) compost. Potential risk to human health was assessed by calculating a bioconcentration factor and a hazard quotient. Results and discussion Overall, the consumption of lettuce and green bean pods grown in some urban gardens posed a potential human health risk due to unacceptably high concentrations of cadmium or lead. In many cases, compost amendment increased the accumulation of metals in the vegetables. Even in soils considered uncontaminated by current guidelines, some hazard quotients exceeded the threshold value of 1. The compost used in this study had a high fulvic acid to humic acid ratio, which may explain increased concentrations of metals in plants grown in compost-amended soils. Conclusions These results indicate a need to include soil characteristics, specifically organic matter quality, when setting threshold criteria for metal content of urban garden soils

Accumulation of Cadmium in Near-Isogenic Lines of Durum Wheat (Triticum Turgidum L. Var Durum): the Role of Transpiration

Concentrations of cadmium in the grain of durum wheat (Triticum turgidum L. var durum) are often above the internationally acceptable limit of 0.2 mg kg−1. Cultivars that vary in concentrations of cadmium in the grain have been identified but the physiology behind differential accumulation has not been determined. Three pairs of near-isogenic lines (isolines) of durum wheat that vary in aboveground cadmium accumulation (8982-TL ‘high’ and ‘low’, W9260-BC ‘high’ and ‘low’, and W9261-BG ‘high’ and ‘low’) were used to test the hypothesis that the greater amounts of cadmium in shoots of the ‘high’ isolines are correlated with greater volumes of water transpired. In general, cadmium content was positively correlated with transpiration only in the ‘low’ isolines. Although shoots of the ‘high’ isolines of W9260-BC and W9261-BG contained higher concentrations of cadmium than did their corresponding ‘low’ isolines, they did not transpire larger volumes of water. In addition, isolines of 8982-TL transpired less water than did the other pairs of isolines yet both ‘high’ and ‘low’ isolines of 8982-TL contained higher amounts of cadmium than did the other pairs. The difference between ‘high’ and ‘low’ isolines appears to be related to the relative contribution of transpiration to cadmium translocation to the shoot. Increased transpiration was associated with increased cadmium content in the ‘low’ isolines but in the ‘high’ isolines increased cadmium in the shoot occurred independently of the volume of water transpired

Production of Organic Acids and Adsorption of Cd on Roots of Durum Wheat (Triticum turgidum L. var. durum)

A number of isolines of durum wheat (Triticum turgidum var durum) differ in their translocation of Cd. In the field, the high isolines accumulate twice the Cd in leaves and grain when compared to the low isolines. The hypothesis that differential accumulation of Cd is associated with differential production of organic acids was tested by measuring Cd content in tissues, Cd partitioning within the root, and organic acids in tissues. In solution culture, the high and low isolines of W9261-BG did not differ in any of the variables measured. Within W9260-BC, the low isoline had half the Cd in its shoot, 30% more tightly-bound Cd in the root and higher concentrations of fumaric, malic, and succinic acids in the root compared to the high isoline. Differential Cd accumulation may be linked to differential adsorption and retention of Cd in the roots of the low Cd-accumulating isolines, possibly via chelation with organic acids

Reduced Translocation of Cadmium from Roots Is Associated with Increased Production of Phytochelatins and Their Precursors

Cadmium (Cd) is a non-essential trace element and its environmental concentrations are approaching toxic levels, especially in some agricultural soils. Understanding how and where Cd is stored in plants is important for ensuring food safety. In this study, we examined two plant species that differ in the distribution of Cd among roots and leaves. Lettuce and barley were grown in nutrient solution under two conditions: chronic (4 weeks) exposure to a low, environmentally relevant concentration (1.0 μM) of Cd and acute (1 h) exposure to a high concentration (5.0 mM) of Cd. Seedlings grown in solution containing 1.0 μM CdCl2 did not show symptoms of toxicity and, at this concentration, 77% of the total Cd was translocated to leaves of lettuce, whereas only 24% of the total Cd was translocated to barley leaves. We tested the hypothesis that differential accumulation of Cd in roots and leaves is related to differential concentrations of phytochelatins (PCs), and its precursor peptides. The amounts of PCs and their precursor peptides in the roots and shoots were measured using HPLC. Each of PC2–4 was synthesized in the barley root upon chronic exposure to Cd and did not increase further upon acute exposure. In the case of lettuce, no PCs were detected in the root given either Cd treatment. The high amounts of PCs produced in barley root could have contributed to preferential retention of Cd in barley roots

Investigating the ability of Pseudomonas fluorescens UW4 to reduce cadmium stress in Lactuca sativa via an intervention in the ethylene biosynthetic pathway

A typical plant response to any biotic or abiotic stress, including cadmium (Cd), involves increased ethylene synthesis, which causes senescence of the affected plant part. Stressed plants can experience reduced ethylene and improved growth if they are inoculated with bacteria that have the enzyme ACC deaminase, which metabolizes the ethylene precursor ACC (1-aminocyclopropane-1-carboxylate). We investigated whether one such bacterium, Pseudomonas fluorescens UW4, reduces the production of ethylene and improves the growth of lettuce (Lactuca sativa) sown in Cd-contaminated potting material (PRO-MIX速 BX). Plants were inoculated with the wild-type P. fluorescens UW4 or a mutant strain that cannot produce ACC deaminase. Cadmium-treated plants contained up to 50 times more Cd than did control plants. In non-inoculated plants, Cd induced a 5-fold increase in ethylene concentration. The wild-type bacterium prevented Cd-induced reductions in root biomass but there was no relationship between Cd treatment and ethylene production in inoculated plants. In contrast, when the concentration of ethylene was plotted against the extent of bacterial colonization of the roots, increased colonization with wild-type P. fluorescens UW4 was associated with 20% less ethylene production. Ours is the first study to show that the protective effect of this bacterium is proportional to the quantity of bacteria on the root surface.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Changes in microbial community structure and increased metal bioavailability in a metal-contaminated soil and in the rhizosphere of corn (Zea mays)

Metal-contaminated soils are common in many urban areas and are potentially toxic to plants and microorganisms. This study investigated metal bioavailability as well as the microbial (i.e., Bacteria and Archaea) functional and structural diversity in the bulk soil and rhizosphere of corn, Zea mays, grown in two metal-contaminated urban soils. The concentrations of bioavailable metals varied between the two soils and increased over time in bulk soil and in the rhizosphere of Zea mays. The microbial communities in bulk and rhizospheric soils metabolized nearly all of the carbon sources on the Ecoplates™ (including amino acids and amines, carbohydrates, carboxylic acids and polymeric compounds), indicating broad degradative capabilities. Terminal restriction fragment length polymorphism (TRFLP) analysis indicated that the two soils contained very different microbial communities and that at day 30 microbial diversity increased in the rhizosphere of both soils. While the presence of Zea mays roots enhanced microbial community diversity in most cases, the physiological potential of the community in the rhizosphere decreased over time in one of the metal-contaminated soils